The invention relates to a polishing-washing method for removing the particles of oxides formed upon working and the particles of removed burrs and cutting metal chips that are left on precision-worked surfaces such as of turbine blades.
The turbine blades are formed, by electrical discharge machining, on the surfaces there of with a concave-shaped pattern receiving a fluid. At the peripheries of the discharge-machined, concave-shaped pattern, there are left the particles of oxides of an alloy used as a base material and the particles of removed burrs and cutting metal chips. In order to remove the particles of the metal oxides of the alloy and the burrs, it has been usual that polishing-washing is carried out by utilizing a water jet or ultrasonic waves while using a polishing media.
The polishing media is in the form of fine particles and is selected from silica, calcium oxide, aluminum oxide, silicon nitride, silicon carbide, cesium oxide, synthetic or natural diamond, metal silicides, tungsten oxide, titanium nitride, titanium oxide, other types of materials that are harder than an alloy used as a constituent base material for the turbine blade, and mixtures thereof.
However, there arise the problems that if a hard polishing media such as of diamond particles is used, the particles may intrude into the surfaces of the base material for the turbine blade and polishing may not proceed satisfactorily when using a relatively soft polishing media.
Further, the particles of metal oxides of an alloy used as a base material for the turbine blade or the particles of removed burrs and cutting metal chips have substantially the same specific gravity as the polishing media, with the attendant problem that it is difficult to separate the particles of the metal oxides and the particles of the removed burrs and cutting metal chips from a polishing media solution composition containing the particles of the metal oxides of the alloy and the particles of the removed burrs and cutting metal chips therein. Further, since the specific gravity of those media is high in respect to water as a fluid, there is a problem that upon making a mixed fluid containing the media, it is difficult to obtain a mixture in which the media remains uniformly mixed in the long term since the media starts to separate indefinably due to different specific gravity and depending on the rate of the media contained in the mixture.
In the practice of the invention, there is provided a polishing-washing method using a hard, light RB ceramic and/or CRB ceramic polishing media, in which a polishing media solution composition is re-used by recycling after subjecting the surfaces of a precision-worked base material to polishing-washing in an efficient manner and simply separating the particles of metal oxides or the particles of removed burrs and cutting metal chips from the polishing media solution composition after the polishing-washing by utilizing the difference in specific gravity.
The polishing-washing method of the invention could solve the above problems, in which an RB ceramic and/or CRB ceramic in the form of a fine power whose bulk specific gravity ranges about 1.20 to 1.40 (g.cmxe2x88x923) (the bulk specific gravity was measured such that the test piece described in JIS R 1601.4 was subjected to the measuring method of bulk specific gravity described in JIS R 7222.7 and it is to be noted that the RB ceramic and/or CRB ceramic is so porous that only a bulk specific gravity can be measured) is used as a polishing media.
More particularly, the RB ceramic and/or CRB ceramic is porous, has such a hardness that the Vickers"" hardness is about 400 or over, can be divided into a fine powder having a size of approximately 1 xcexcm, is not so hard as diamond and is not thus intruded into an alloy in the surface of a base material, and is small in bulk specific gravity. Accordingly, if such a ceramic is dispersed in an aqueous surfactant solution having substantially the same specific gravity to provide a polishing media solution composition, the particles of metal oxides and particles of removed burrs and cutting metal chips can be settled only by allowing the solution to stand after polishing-washing. The removal of the resultant precipitate by filtration makes it possible to provide a refreshed polishing media solution composition for recycling.
The RB ceramic and CRB ceramic used in the invention are those materials prepared according to the following process.
The porous carbon material that is obtained by using rice bran produced at 900,000 tons per year in Japan and at 33,000,000 tons per year in the world is known according to the studies made by Kazuo HOKKIRIGAWA, one of the co-inventors of this application (see xe2x80x9cFunctional Materialsxe2x80x9d May 1997, Vol. 17, No. 5, Pp. 24 to 28).
In this literature, reference is made to a carbon material (hereinafter referred to as RB ceramic) and the preparation thereof, wherein the material is obtained by blending and kneading defatted bran derived from rice bran and a thermosetting resin, followed by drying a molded compact obtained by pressure forming and subsequently baking the dried compact in an atmosphere of an inert gas.
According to this method, the difference in contraction ratio between the size of the pressure-formed compact and the size of the final molded compact obtained by baking in the inert gas atmosphere is at 25%, which makes it substantially difficult to make a precise molded compact. A ceramic (CRB ceramic) improved in the ratio has now been developed. The RB ceramic and the CRB ceramic individually have the following general properties.
Higher hardness.
Smaller expansion coefficient.
Porous microstructure.
Good Electrical conductivity.
Small bulk density and light weight.
Good abrasion resistance.
Easy to form and easy to fabricate in a die.
The ceramic can be divided into fine powder.
The materials being made of rice bran, they have little adverse effect on the global environment, leading to conservation of natural resources.
The CRB ceramic used in the invention is an improved material of the RB ceramic that is obtained from defatted bran, derived from rice bran, and a thermosetting resin. More particularly, the defatted bran derived from rice bran and a thermosetting resin are mixed and kneaded and subjected to primary baking in an inert gas at a temperature range of 700xc2x0 C. to 1000xc2x0 C., pulverizing the kneaded mixture after the primary baking into carbonized powders passing through a sieve at a level of 60 mesh or below. The carbonized powder and a thermosetting resin are further mixed and kneaded, and pressure formed at a pressure of 20 Mpa to 30 Mpa, and subjecting the compact again to a heat treatment in an inert gas at a temperature range of 100xc2x0 C. to 1100xc2x0 C. to obtain a black resin or porous ceramic. The greatest difference from the RB ceramic resides in that while the contraction ratio between the size of a final compact and the size at the time of molding of the RB ceramic is as large as 25%, the CRB ceramic is excellent in that the ratio is as small as 3% or below. In the invention, however, compacts are not made and a fine powder is used, so that such a difference is not utilized at all. In this sense, either the RB ceramic or CRB ceramic can be fundamentally used.
In the RB ceramic and/or CRB ceramic used in the invention, the specific gravity thereof is important: this is greatly influenced by the primary baking temperature for the RB ceramic and the primary baking temperature and the secondary heat treatment temperature for the CRB ceramic.
Generally, a higher primary baking temperature and a higher secondary heat treatment temperature result in an RB ceramic or CRB ceramic having a smaller specific gravity.